1. Field of the Invention
The present invention relates to a seek control apparatus which performs seek control of a magnetic disk drive and a method for generating control data for seek control.
2. Related Art
Seeking a relatively small number of tracks of a magnetic disk with respect to the total servo tracks is generally called short seek.
To control short seeks, a conventional two-degree-of-freedom control system which uses a positioning feedback controller and a feed-forward controller is often used because the system readily reduces seek period which is a time period to required to seek.
In a short seek control system of a real-world magnetic disk drive, an acceleration input value for feed-forward control and a position trajectory (target trajectory) followed when the acceleration input value is input in a voice coil motor (VCM) plant model (Formula E, which will be described later) are calculated off-line beforehand and the calculated acceleration input value and target trajectory are stored as a numerical table in memory of a microprocessor which executes the short seek control system.
During seek control, a feed-forward control system can be implemented by referring to values in the table at each sample time. Deadbeat control (bang-bang control) is generally used in the feed-forward input (acceleration input). The plant model of the VCM used for calculating beforehand the values in the table for the feed-forward control system described above consists of the product of a second-order integral and a model gain.
Different magnetic disk drives, which are mass-produced, have different VCM gains. In addition, since the feed-forward control system is configured on the basis of a simplified model of a voice coil motor in which many mechanical resonances are inherently present, there are modeling errors. VCM gain variations and modeling errors degrade seek response during seek control and frequently cause write errors during settling (the sample time at the end of the seek control). In order to reduce seek period, it is desirable that the number of traversed tracks to which the short seek control system is applied be increased. However, as the traversed distance increases, more errors are caused by modeling errors and seek response degradation by excitation of mechanical resonance of the arm that supports the head becomes more serious.